As with any third-party integration, we are forced to work within the parameters set by that party. LawVu integrates with Microsoft Outlook via the LawVu add-in.

Due to increased usage by users in remote work scenarios, Microsoft has taken measures to ensure their critical services remain available and reliable. They have, therefore, as of June 1, 2020, introduced tighter throttling limits.

Throttling limits the number of concurrent calls to a service to prevent the overuse of resources and helps maintain optimal performance and reliability despite a high volume of requests.

The most common cause of throttling is making a large number of requests in a short time span.

"When a throttling threshold is exceeded, Microsoft Graph limits any further requests from that client for a period of time. When throttling occurs, Microsoft Graph returns HTTP status code 429 (Too many requests), and the requests fail. A suggested wait time is returned in the response header of the failed request. Throttling behavior can depend on the type and number of requests. For example, if you have a high volume of requests, all requests types are throttled. Threshold limits vary based on the request type. Therefore, you could encounter a scenario where writes are throttled but reads are still permitted."

Outlook service limits

"Outlook service limits are evaluated for each app ID and mailbox combination. In other words, the limits described apply to a specific app accessing a specific mailbox (user or group). If an application exceeds the limit in one mailbox, it does not affect the ability to access another mailbox. The following limits apply to the public cloud as well as national cloud deployments:

10,000 API requests in a 10 minute period v1.0 and beta endpoints

4 concurrent requests v1.0 and beta endpoints

15 megabit upload (PATCH, POST, PUT) in a 30 second period"

https://docs.microsoft.com/en-nz/graph/throttling#outlook-service-limits